An investigation was conducted on the effect of frost fonnation on the perfonnance
evaporator coils typically found in domestic refrigerator-freezers. The effect of fin spacing
on evaporator perfonnance was also studied. The study was carried out by setting the
conditions of air inlet temperature, air inlet relative humidity, and refrigerant inlet
temperature, and by varying the volumetric airflow rate over a wide range to study its effect
on the evaporator overall heat transfer coefficient and the evaporator pressure drop. These
values were monitored while frost accumulated on the evaporator over a ten hour period.
The data was modeled using a least-squares curve fit where the heat transfer coefficient and
the pressure drop were taken to be functions of the airflow rate and the mass of
accumulated frost. Using a characteristic fan curve and the models for the heat transfer
coefficient and pressure drop, conditions closely emulating actual systems were simulated
and the actual variation of heat transfer coefficient as a function of accumulated frost was
found It showed the expected trend of rising to a point and then dropping off. The overall
heat transfer coefficient increased up to 40% of its starting value and was reached after the
airflow rate had decreased to about 70% of its starting value. These were dependent on the
fan characteristic curve that was used. The effect of fin spacing was studied by comparing
a 5 fin per inch evaporator to a 2.5 fin per inch evaporator. The overall heat transfer
coefficient was found to be directly proportional to the air-side surface area but the amount
of frost deposited did not show this trend.

Issue Date:

1992-02

Publisher:

Air Conditioning and Refrigeration Center. College of Engineering. University of Illinois at Urbana-Champaign.